The present invention relates to a method for making organic carbonates by reacting an organic hydroxy compound, such as phenol, with carbon monoxide and oxygen in the presence of a palladium catalyst, a quaternary ammonium salt, and a cocatalyst of a metallic material, such as a cobalt salt, and an organic material such as benzophenone. More particularly, the present invention relates to a method for making diphenyl carbonate which provides a means for recycling catalyst values and minimizes the production of color bodies resulting from the decomposition of particular organic cocatalyst components.
J. E. Backvall, et al, show in their publication, Biomimetic Aerobic 1,4-Oxidation of 1,3-Dienes Catalyzed by Cobalt Tetraphenylporphyrin-Hydroquinone-Palladium (II), An Example of Triple Catalysis, J. Am. Chem. Soc. 1987, 109, 4750-4752, the use of macrocyclic metal complexes employing p-benzoquinone-hydroquinone as a catalytic electron carrier in oxidation reactions and palladium catalyzed oxidations of conjugated dienes. There also is shown by T. C. T. Chang, copending application Ser. No. 07/607,773, a method for making organic carbonates utilizing an organic hydroxy compound with carbon monoxide and oxygen and a catalyst in the form of elemental or chemically combined palladium, cobalt, tetraalkylammonium halide and at least one quinone, an aromatic diol reduction product or mixture thereof. In T. C. T. Chang copending application Ser. No. 217,248, filed Jul. 11, 1988, there is shown a method of making organic carbonates utilizing a similar procedure as Ser. No. 07/607,773 except that in place of chemically combined cobalt, there is utilized divalent or trivalent manganese.
In copending application 07/503,404, filed Apr. 2, 1990, there is shown a method for making organic carbonates employing an organic hydroxy compound, such as phenol, carbon monoxide and oxygen in the presence of an effective amount of a palladium catalyst and carbon dioxide as a desiccant. As taught in Ser. No. 07/503,404, there can be used in combination with the palladium catalyst, such as palladium(II) acetate, a tetraalkylammonium halide and at least one quinone and aromatic diol formed by the reduction of said quinone or a mixture thereof. In addition, a manganese or cobalt cocatalyst also can be used.
Although the aforementioned methods for making organic carbonates are of interest because they do not require the use of phosgene which is a toxic and irritating gas, experience has shown that recycling of catalyst values and/or recovery of the organic carbonate free of color bodies is often not feasible. It is believed that the use of quinones such as hydroquinones causes catalyst deactivation. Attempts to recycle catalyst values free of impurities after separation of organic carbonate is rendered difficult because of the quinone breakdown during carbonylation. It would be desirable therefore to provide a method for making organic carbonates without the use of phosgene, while permitting a recycling of catalyst values, along with a simplified recovery of product free of color bodies.